A microwave oven having synchronously rotatable reflectors

ABSTRACT

A microwave oven with a waveguide for supplying microwave energy to the oven cavity. A magnetron antenna projects into the waveguide. A pair of cyclically rotatable reflectors are located on opposite sides of the antenna within the waveguide. The reflectors are positioned and shaped so as to reflect microwave energy back to the magnetron with a given phase lag so as to cause the magnetron to operate in the sink range.

United States Patent Wikstrom et a1.

[ June 26, 1973 [5 MICROWAVE OVEN HAVING 2/1972 lkeda 219/1055 SYNCHRONOUSLY ROTATABLE 2,910,566 10/1959 Smith 219/1055 REFLECTORS [75] Inventors: Stellan Brynolf Wikstrom, Primary Examiner-J. V. Truhe Sundbyberg; Leo Malmquist, Assistant Examiner-Hugh D. Jaeger Ektorp, both of Sweden AttorneyFrank R. Trifari [73] Assignee: U.S. Philips Corporation, New York,

57 ABSTRACT [22] Filed: Jan. 10, 1972 1 2 App] 2 5 A microwave oven with a waveguide for supplying mi crowave energy to the oven cavity. A magnetron antenna projects into the waveguide. A pair of cyclically [52] U.S. Cl. 219/10-55 rotatable reflectors are located on opposite Sides of the [51] Int. Cl. 1105b 9/06 antenna within the waveguide The reflectors are posi [58] Field of Search 219/1055 tioned and Shaped so as to reflect microwaveenergy back to the magnetron with a given phase lag so as to [56] References C'ted cause the magnetron to operate in the sink range.

UNITED STATES PATENTS 2,909,635 10/1959 Haagensen 219/1055 13 Claims, 4 Drawing Figures PATENTEU JUN 2 6 I973 sum-1mg Fig.3

PATENTED JUN 26 I975 SHEEYZUFZ Fig.2

A MICROWAVE OVEN HAVING SYNCHRONOUSLY ROTATABLE REFLECTORS This invention relates to a microwave oven comprising an oven cavity, a magnetron and a supply wave guide system in the shape of a continuous slot shaped space situated outside the side walls of the cavity, into which space an antenna of the magnetron projects. In order to feed microwave energy into the cavity, at least one of the walls separating the cavity from the wave guide system is provided with slit shaped openings through which the microwave energy radiates into the cavity. The object is in particular to achieve in a microwave oven of this kind a simple and effective distributing arrangement which ensures an even energy distribution in the cavity.

The characteristic feature of the invention consists in that in the wave guide system, on at least one side, preferably on both sides, of the antenna as seen in the propagation direction for the energy, are arranged reflector bodies which are cyclically variable to a different degree of reflection. The reflector bodies are so shaped and placed that the magnetron at, least during the main part of the operation cycle for the reflector bodies, will receive a reflected wave in such a phase position that the magnetron operates substantially in the sink range.

By the reflection against the bodies a standing wave will arise in the wave guide system surrounding the cavity, which standing wave due to the cyclic variation of the bodies will vary as to size and phase. In the preferred embodiment having reflector bodies arranged on both sides of the antenna, the effect will be that the energy is thrown alternately in the one and the other direction, whereby maximal variation of the standing wave pattern can be reached during the motion cycle of the bodies, which in combination with the distributed energy supply into the cavity will produce an even energy distribution in the same. At the same time it is possible by a suitable shape of the bodies and a synchronous driving of the bodies to ensure that the wave reflected back to the magnetronwill not atany moment have an unallowable size so that the magnetron is damaged. The localization of the reflecting bodies in such manner that the magnetron operates substantially in the sink range furthermore insures that the magnetron during the whole motion cycle will operate at a high power level.

In a preferred embodiment of the device according to the invention the reflector bodies are rotatably arranged on axes which are perpendicular to the propagation direction of the energy in the wave guide system. Hereby the point of reflection will move in a direction to and from the antenna of the magnetron, whereby the phase position of the reflected wave will vary periodically. The field maximum for the standing wave resulting from the reflection will thus move along the wave guide system, which will produce a more even energy distribution in the oven. A contributing cause to the improved distribution of the energy is that in certain positions of the movable bodies certain higher modes will arise. A certain frequency variation, which is most pronounced when the magnetron operates in the sink range, will also contribute to the improved energy distribution.

The invention is illustrated in the accompanying drawings in which:

FIGS. 1-3 show schematic views-of the wave guide system in an oven provided with a device according to the invention, FIG. 1 being a vertical sectional view, FIG. 2 a sectional view as seen from the side of the oven along the line AA in FIG. 1 and FIG. 3 a sectional view as seen from above along the line B-B in FIG. I, and

FIG. 4 shows an alternative shape of the reflector bodies in .the ovenaccording to FIGS. 1-3.

As shown in FIG. 1 an oven cavity 10 is defined by a bottom plate 11 and a top plate 13, and side walls 12 and 14. An outer envelope 15 consists of a top plate 16 and side walls 17 and 18. Below the bottom plate of the cavity there is a further plate 19 which is attached to the outer envelope. At the front side and rear side the construction is closed by walls 20, 21 (see FIG. 2 and 3) which in this schematic embodiment can be regarded as common for the cavity and the outer envelope.

According to FIG. 1 the outer envelope, including the said further plate 19, is at all sides of the cavity at a distance from the walls of the cavity so that outside the cavity are formed slot shaped communicating spaces 22, 23, 24, 25. These spaces form together a supply wave guide for feeding microwave energy from a magnetron, which is schematically indicated at 26, to the cavity 10. The antenna 27 of the magnetron projects for this purpose into the lower waveguide space 22. The energy will propagate from the antenna in both directions and further through the side spaces 23, 25 to the upper space 24. For feeding energy from the wave guide system to the inside of the cavity 10, slits 28 are cut in both the bottom plate and the top. plate of the cavity, as seen in FIG. 3 where the central part of the cavity is removed for illustrative purposes. The oven may, for example, be constructed in the manner described in the copending US. Pat. application Ser. No. 208,599, filed Dec. 16, 1971, where the magnetron is mounted on the underside of a lid (corresponding to the bottom plate 19 in FIGS. 1 and 2) to a container which, besides the magnetron, contains the whole electrical supply circuit for the magnetron and which container is suitably filled with oil or the like according to the aforesaid patent application.

According to the invention, variable reflector bodies 30, 31 are arranged on both sides of the magnetron antenna, as' seen in the direction of propagation-of the microwave energy. The reflector bodies are composed of electrically conductive material and, according to FIG. 3, each consists of two wings 32, 33 and 34, 35, respectively. The reflector bodies are arranged with their length direction perpendicular to the propagation direction of the energy in the wave guide system and they are rotatably mounted on shafts 36, 37. The wings on each body are arranged with a fixed mutual angle of I-Iereby during the rotation one of the wings will always have minimum reflection when the second wing has maximum reflection and vice versa. The reflector bodies are driven synchronously in the same rotation direction, for example, by means of a common driving wheel. The driving mechanism is such that the bodies rotate with a mutual phase difference of about 45.

The reflector bodies give rise to reflected waves in the direction back towards the magnetron antenna, the phase position of which are determined by the distance between the antenna and the reflectorbodies. In a certain phase position of the reflected wave the magnetron will operatein the so called sink range, where it delivera a high output power. The said distance between-the antenna and the reflector bodies is then adjusted so that the magnetron operates substantially in the sink range for all angular positions of the reflector bodies. Due to the variation in distance to the reflecting point upon rotation of the bodies, the operation point will vary somewhat with the angular position of the bodies, but it has been proved that in the described embodiment the said distance can be selected such that a resulting wave is obtained which causes the magnetron to operate at least approximately in the sink range for all positions of the reflector bodies. Due to the frequency spread between different magnetrons it cannot be prevented that in certain positions of the reflector bodies, at frequencies which deviate essentially from nominal frequency, that the operation point during some part of the cycle will fall in the range for anti-sink. However, even in these extreme cases the operation point will fall in the sink range during the main part of the rotation period for the reflector bodies.

The width of the wings should in first hand be adapted to the width of the space 22 so that at maximal reflection a-heavy standing wave is achieved, but they can also be selected in a special manner relative to the wave length of the energy, for example, equal to a multiple of a quarter of a wave length.

The function of the device is that the reflector bodies will produce reflected waves back to the antenna of the magnetron, which waves will propagate past the opposite reflector body and result in a standing wave in the whole wave guide system. At any moment, the synchronous drive and mutually fixed angular setting of the bodies have the effect of preventing the reflected wave from assuming an unallowable size that might damage the magnetron. At the same time as the reflection dethe standing wave pattern means that the points where the field strength is maximal along the wave guide system will move relative to the slits through which the energy radiates into the cavity. At some occasion one slit will have maximal radiation and at some other occasion another slit will have maximal radiation, which contributes to an improved energy distribution within the cavity. In certain positions of the reflector bodies oscillation modes of higher order can arise and be extinguished, respectively, which can also contribute to an improved energy distribution. A certain frequency variation of the magnetron for different angular positions of the reflector bodies can also contribute to a variation of the standing wave pattern and thereby an improved energy distribution.

FIG. 4 shows an alternative embodiment of the reflector bodies, where instead of perpendicular wings the body has a helicoidal shape. The pitch of the helicoid is in the example such that the two end sections of the body will be at 90 relative to each other. Alternatively the helicoid can have another pitch. Even quite different shapes of the reflector bodies are possible within the scope of the invention. Thus, the bodies may, for example, consist of plane disks having different width according to a suitable pattern as seen in the length direction. In principle, one single reflector body also can be arranged on one side of the antenna, in which case the effect will be similar to that described in the foregoing relating to two bodies, namely a standing wave which is displaced along the wave guide sys tem even if, in this case, it will be more difficult to get a sufficient variation in the standing wave pattern for achieving an even energy distribution.

What is claimed is:

ll. A microwave oven comprising, means defining an oven heating cavity with side walls, a magnetron, means defining a wave guide system having the shape of a continuous slot shaped space situated outside the side walls of the oven cavity, means for locating the magnetron so that an antenna of the magnetron projects into said waveguide space, at least one of the side walls between the oven cavity and the wave guide system being provided with a plurality of slit shaped openings thereby to provide a passage for the microwave energy into the oven cavity, at least one energy reflector body located in the wave guide system on one side of the antenna as seen in the direction of propagation of the microwave energy in the waveguide system, means for cyclically varying said reflector body to different degrees of reflection, said reflector body being shaped and located so that the magnetron receives a reflected wave therefrom during at least the main part of the operation cycle of the reflector body with a phase position such that the magnetron operates substantially in the sink range.

2. A microwave oven as claimed in claim 11 further comprising a second energy reflector body located in the waveguide system on the opposite side of the an tenna as seen in the direction of propagation of the microwave energy therein, means for cyclically varying said second reflector body, the reflector bodies being shaped so that they have different reflecting properties as seen in a direction perpendicular to the propagation direction of the energy.

3. A microwave oven as claimed in claim 2, wherein said body varying means include means for rotating the reflector bodies about axes which are perpendicular to the propagation direction of the waveguide energy.

d. A microwave oven as claimed in claim 2 further comprising means for synchronously driving the reflector bodies with a certain constant mutual phase displacement therebetween.

5. A microwave oven as claimed in claim 4, characterized in that the reflector bodies are shaped like two or more flat wings having different mutual angular positions about the respective axes of rotation.

d. A microwave oven as claimed in ciaim 5, characterized in that each reflector body comprises two wings each covering approximately half the width of the wave guide, said wings having a mutual angle of substantially 7. A microwave oven as claimed in claim ti, wherein said driving means is arranged to drive the reflector bodies with a mutual phase displacement of substantially 45.

8. An arrangement as claimed in claim 2 characterized in that the reflector bodies have a helical shape.

9. A microwave oven comprising, means defining an oven heating cavity with side walls, means defining a waveguide with walls outside of and adjacent to but spaced from the walls of the oven cavity to form therewith an enclosed waveguide system, a magnetron having an antenna projecting into said waveguide, at least one waveguide defining wall of the oven cavity including a plurality of elongated openings therein through which the microwave energy is supplied to the oven cavity, first and second energy reflectors located within the waveguide on opposite sides of the antenna, means for cyclically varying the reflectors so as to'cyclically change the energy reflected thereby, said reflector bodies being shaped and located so that the energy reflected therefrom towards the'magnetron causes thewave energy is supplied to of the oven cavity, said waveguide including the side walls and the top wall of the oven cavity and the container, and said top and bottom oven cavity walls each include a plurality of elongated openings through which microwave energy is supplied to the oven cavity.

12. A microwave oven as claimed in claim 9 wherein said reflector varying means includes means for synchronously rotating the reflectors with a predetermined fixed mutual phase displacement therebetween.

13. A microwave oven as claimed in claim 1 wherein said waveguide defining means comprise a metal container enclosing said oven cavity, said antenna and reflector body being located opposite the bottom wall of the oven cavity, said waveguide including the side walls and the top wall of the oven cavity and the container, and said top and bottom oven cavity walls each include a plurality of elongated openings through which microthe oven cavity.

2 33" UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,742,177 Dated June 26, 1973 Inventor(s) STELLAN BRYNOLF WIKS'I'ROM ET AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

col. 2, line 3, cancel "A-A" and ins ert II-II line 4, cancel "B- B and insert III -III IN THE CLAIMS col. 4, line 61, cancel "An arrangement" and insert A microwave oven Signed and sealed this 27th day of November- 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,J'R. v RENE D. TEGTMEYER Attes ting Officer Acting Commissioner of Patents 72x 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,742,177 Dated une 1973 Inventofls) STELLAN BRYNOLF WIKSTRQM ET AL I It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

O v I n col. 2, line 3, cancel "A-A" and insert II-II line 4, cancel "B -B" and insert IIIE-III IN THE CLAIMS col. 4, line 61, cancel "An arrangement" and insert A microwave oven Signed and sealed this 27th day of November 1973 (SEAL) Attest: H

EDWARD M.FLETCHER,JR. I RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents 

1. A microwave oven comprising, means defining an oven heating cavity with side walls, a magnetron, means defining a wave guide system having the shape of a continuous slot shaped space situated outside the side walls of the oven cavity, means for locating the magnetron so that an antenna of the magnetron projects into said waveguide space, at least one of the side walls between the oven cavity and the wave guide system being provided with a plurality of slit shaped openings thereby to provide a passage for the microwave energy into the oven cavity, at least one energy reflector body located in the wave guide system on one side of the antenna as seen in the direction of propagation of the microwave energy in the waveguide system, means for cyclically varying said reflector body to different degrees of reflection, said reflector body being shaped and located so that the magnetron receives a reflected wave therefrom during at least the main part of the operation cycle of the reflector body with a phase position such that the magnetron operates substantially in the sink range.
 2. A microwave oven as claimed in claim 1 further comprising a second energy reflector body located in the waveguide system on the opposite side of the antenna as seen in the direction of propagation of the microwave energy therein, means for cyclically varying said second reflector body, the reflector bodies being shaped so that they have different reflecting properties as seen in a direction perpendicular to the propagation direction of the energy.
 3. A microwave oven as claimed in claim 2, wherein said body varying means include means for rotating the reflector bodies about axes which are perpendicular to the propagation direction of the waveguide energy.
 4. A microwave oven as claimed in claim 2 further comprising means for synchronously driving the reflector bodies with a certain constant mutual phase displacement therebetween.
 5. A microwave oven as claimed in claim 4, characterized in that the reflector bodies are shaped like two or more flat wings having different mutual angular positions about the respective axes of rotation.
 6. A microwave oven as claimed in claim 5, characterized in that each reflector body comprises two wings each covering approximately half the width of the wave guide, said wings having a mutual angle of substantially 90*.
 7. A microwave oven as claimed in claim 6, wherein said driving means is arranged to drive the reflector bodies with a mutual phase displacement of substantially 45*.
 8. An arrangement as claimed in claim 2 characterized in that the reflector bodies have a helical shape.
 9. A microwave oven comprising, means defining an oven heating cavity with side walls, means defining a waveguide with walls outside of and adjacent to but spaced from the walls of the oven cavity to form therewith an enclosed waveguide system, a magnetron having an antenna projecting into said waveguide, at least one waveguide defining wall of the oven cavity including a plurality of elongated openings therein through which the microwave energy is supplied to the oven cavity, first and second energy reflectors located within the waveguide on opposite sides of the antenna, means for cyclically varying the reflectors so as to cyclically change the energy reflected thereby, said reflector bodies being shaped and located so that the energy reflected therefrom towards the magnetron causes the magnetron to operate in the sink range for a major portion of the operating cycle of the oven.
 10. A microwave oven as claimed in claim 9 wherein said reflector varying means includes means for rotating the reflectors about axes of rotation that are parallel to one another and orthogonal to the longitudinal axis of the antenna.
 11. A microwave oven as claimed in claim 9 wherein said waveguide defining means comprise a metal container enclosing said oven cavity, said antenna and reflector bodies being located opposite the bottom wall of the oven cavity, said waveguide including the side walls and the top wall of the oven cavity and the container, and said top and bottom oven cavity walls each include a plurality of elongated openings through which microwave energy is supplied to the oven cavity.
 12. A microwave oven as claimed in claim 9 wherein said reflector varying means includes means for synchronously rotating the reflectors with a predetermined fixed mutual phase displacement therebetween.
 13. A microwave oven as claimed in claim 1 wherein said waveguide defining means comprise a metal container enclosing said oven cavity, said antenna and reflector body being located opposite the bottom wall of the oven cavity, said waveguide including the side walls and the top wall of the oven cavity and the container, and said top and bottom oven cavity walls each include a plurality of elongated openings through which microwave energy is supplied to the oven cavity. 